This invention relates to a catalyst for the gasification of heavy hydrocarbons. More particularly, the invention relates to a catalyst which is used for the catalytic gasification of relatively heavy hydrocarbons in a fluidized catalytic bed.
It is well known in the conventional art that relatively heavy hydrocarbons such as the residual oils of atmospheric distillation or reduced pressure distillation are subjected to catalytic cracking in a fluidized bed to produce fuel gas, town gas and raw material gas for industrial purposes.
The catalyst particles for such fluidized bed are brought into contact with reactants (raw oils) in a fluidized state, so that the necessary properties for the fluidized bed catalyst are somewhat different from those of the catalyst for fixed bed operation.
For instance, the fixed bed catalyst must have the properties of (1) high catalytic activity (high efficiency in water gas shift reaction), (2) good selectivity, (3) large mechanical strength, and (4) long catalytic life.
Needless to say, the catalyst particles for the fluidized bed must also have the above-mentioned properties, it is still necessary to have some specific properties in addition to the above.
That is, the particles of fluidized bed catalyst should be resistant to wear because they collide repeatedly with each other and with the interior wall of reaction tube in a fluidized state.
Further, in order to maintain the fluidized state successfully, the catalyst particles should have a proper particle size distribution and each particle may be almost spherical.
In some instances, heavy hydrocarbon oil was subjected to catalytic cracking in fluidized beds to produce gas, however, there has never been reported the catalyst which satisfies the above-mentioned requirements.
It is well known that calcium oxide (CaO) has catalytic activity for the water gas reaction of heavy hydrocarbons. The purpose in using free calcium oxide particles resides in the fixation of sulfur vanadium, sodium and the like contained in the raw oil, as well as in the utility of the catalytic activity for water gas reaction. When the calcium oxide particles are used as catalyst, however, the following disadvantage is occur.
Calcium oxide particles absorb H.sub.2 O and CO.sub.2 and decaying particles, the so-called slaking, takes place. Calcium oxide is usually obtained by calcining limestone or dolomite at a temperature above 900.degree. C. and is generally used in the form of powdery particles. However, when these calcium oxide particles are used for fluidized bed operation, the smooth flow of the particles can not be expected since the particle size distribution of such calcium oxide is not covered within a certain range.
Furthermore, owing to the lack of wear resistance and to the above-mentioned disintegration by slaking, the calcium oxide particles are liable to become fine powder. The produced powder is caused to fly off or it forms secondary agglomerates which prevents the catalyst particles from smooth flowing in the reaction tube.
Still further, as disclosed in the above, calcium oxide fixes sulfur and heavy metals such as nickel and vanadium contained in the raw material oil, and this fact means that the calcium oxide catalyst is poisoned by sulfur and heavy metals. Thus the catalytic activity is decreased and the catalytic life becomes short, which have been serious problems in the conventional art.